In power conversion equipment, power regulation is sometimes implemented on the primary side of a transformer which is used to provide isolation of the load from a power source. Virtually all power control equipment requiring isolated feedback from the load use either a feedback transformer or an optical transmission medium.
In the first instance, a feedback transformer is used in addition to the power transformer. Feedback signals are transmitted to the primary control circuit, via the feedback transformer. This signal includes information which may be in the form of a stream of digital pulses or a continuously variable amplitude modulated signal.
With the second of these feedback schemes, an optical coupler is used as a transmission medium and provides a feedback path while maintaining isolation. The feedback signal as in the first instance, may be in the form of a stream of digital pulses of light or an analog signal which varies in intensity continuously.
The problem associated with the above feedback schemes, is that they require a separate isolated feedback loop, making these expensive to implement and manufacture.